1. Field of the Invention
The present invention relates to a battery unit in which battery arms are connected in parallel, and to a battery system using the battery unit.
2. Description of the Related Art
In a conventional battery system, a battery charge/discharge switching method has been known, which is capable of achieving reduction in size, weight and cost by omitting or downsizing a cooling device while reducing a conduction loss to a semiconductor switch, and is capable of eliminating an occurrence of mechanical abrasion or operation sounds, which follow frequent on/off operations of a mechanical contact switch (refer to Japanese Patent Laid-Open Publication No. 2007-110887 as Patent Publication 1).
In this battery charge/discharge switching method, a charge/discharge switching circuit in which the mechanical contact switch, the semiconductor switch and a diode are connected in parallel is connected in series to each of batteries. Then, at a discharging time when a large current is passed and in an operation range of charging the large current, the current is passed by means of the mechanical contact switch, whereby the conduction loss is reduced. Meanwhile, in an operation range of charging a small current, the current is passed by means of the semiconductor switch, whereby the conduction loss is reduced. With such a configuration, the operation sounds caused by on/off operations in a pulse charge and by an off operation at the time when the charge is completed are suppressed.